NOx reduction compositions for use in FCC processes

ABSTRACT

Compositions for reduction of gas phase reduced nitrogen species and NO x  generated during a partial or incomplete combustion catalytic cracking process, preferably, a fluid catalytic cracking process, are disclosed. The compositions comprise (i) an acidic metal oxide containing substantially no zeolite, (ii) an alkali metal, alkaline earth metal, and mixtures thereof, (iii) an oxygen storage component, and (iv) a noble metal component, preferably rhodium or iridium, and mixtures thereof, are disclosed. Preferably, the compositions are used as separate additives particles circulated along with the circulating FCC catalyst inventory. Reduced emissions of gas phase reduced nitrogen species and NO x  in an effluent off gas of a partial or incomplete combustion FCC regenerator provide for an overall NO x  reduction as the effluent gas stream is passed from the FCC regenerator to a CO boiler, whereby as CO is oxidized to CO 2  a lesser amount of the reduced nitrogen species is oxidized to NO x .

FIELD OF THE INVENTION

The present invention relates to NO_(x) reduction compositions and themethod of use thereof to reduce NO_(x) emissions in refinery processes,and specifically in fluid catalytic cracking (FCC) processes. Moreparticularly, the present invention relates to NO_(x) reductioncompositions and their method of use to reduce the content of gas phasereduced nitrogen species in FCC regenerator off gases released from afluid catalytic cracking unit (FCCU) regenerator operating in a partialor incomplete combustion mode.

BACKGROUND OF THE INVENTION

In recent years there has been an increased concern in the United Statesand elsewhere about air pollution from industrial emissions of noxiousoxides of nitrogen, sulfur and carbon. In response to such concerns,government agencies have in some cases already placed limits onallowable emissions of one or more of the pollutants, and the trend isclearly in the direction of increasingly stringent restrictions.

NO_(x), or oxides of nitrogen, in flue gas streams exiting from fluidcatalytic cracking (FCC) regenerators is a pervasive problem. Fluidcatalytic cracking units (FCCU) process heavy hydrocarbon feedscontaining nitrogen compounds a portion of which is contained in thecoke on the catalyst as it enters the regenerator. Some of this cokenitrogen is eventually converted into NO_(x) emissions, either in theFCC regenerator or in a downstream CO boiler. Thus all FCCUs processingnitrogen-containing feeds can have a NO_(x) emissions problem due tocatalyst regeneration.

In an FCC process, catalyst particles (inventory) are repeatedlycirculated between a catalytic cracking zone and a catalyst regenerationzone. During regeneration, coke from the cracking reaction deposits onthe catalyst particles and is removed at elevated temperatures byoxidation with oxygen containing gases such as air. The removal of cokedeposits restores the activity of the catalyst particles to the pointwhere they can be reused in the cracking reaction. The coke removal stepis performed over a wide range of oxygen conditions. At the minimum,there is typically at least enough oxygen to convert essentially all ofthe coke made to CO and H₂O. At the maximum, the amount of oxygenavailable is equal to or greater than the amount necessary to oxidizeessentially all of the coke to CO₂ and H₂O.

In an FCC unit operating with sufficient air to convert essentially allof the coke on the catalyst to CO₂ and H₂O, the gas effluent exiting theregenerator will contain “excess oxygen” (typically 0.5 to 4% of totaloff gas). This combustion mode of operation is usually called “fullburn”. When the FCCU regenerator is operating in full burn mode, theconditions in the regenerator are for the most part oxidizing. That is,there is at least enough oxygen to convert (burn) all reducing gas phasespecies (e.g., CO, ammonia, HCN) regardless of whether this actuallyhappens during the residence time of these species in the regenerator.Under these conditions, essentially all of the nitrogen deposited withcoke on'the catalyst during the cracking process in the FCCU riser iseventually converted to molecular nitrogen or NO_(x) and exits theregenerator as such with the off gas. The amount of coke nitrogenconverted to NO_(x) as opposed to molecular nitrogen depends on thedesign, conditions and operation of the FCCU, and especially of theregenerator, but typically the majority of coke nitrogen exits theregenerator as molecular nitrogen.

On the other hand, when the amount of air added to the FCCU regeneratoris insufficient to fully oxidize the coke on the cracking catalyst toCO₂ and H₂O, some of the coke remains on the catalyst, while asignificant portion of the burnt coke carbon is oxidized only to CO. InFCCUs operating in this fashion, oxygen may or may not be present in theregenerator off gas. However, should any oxygen be present in theregenerator off gas, it is typically not enough to convert all of the COin a gas stream to CO₂ according to the chemical stoichiometry ofCO+{fraction (1/2)}O₂→CO₂This mode of operation is usually called “partial burn.” When an FCC Uregenerator is operating in partial burn mode, the CO produced, a knownpollutant, cannot be discharged untreated to the atmosphere. To removethe CO from the regenerator off gas and realize the benefits ofrecovering the heat associated with burning it, refiners typically burnthe CO in the regenerator off gas with the assistance of added fuel andair in a burner usually referred to as “the CO boiler”. The heatrecovered by burning the CO is used to generate steam.

When the regenerator is operating in partial burn, the conditions in theregenerator, where the oxygen added with air has been depleted and COconcentration has built up, are overall reducing. That is, there is notenough oxygen to convert/burn all reducing species regardless if someoxygen is actually still present. Under these conditions some of thenitrogen in the coke is converted to so called “gas phase reducednitrogen species”, examples of which are ammonia and HCN. Small amountsof NO_(x) may also be present in the partial burn regenerator off gas.When these gas phase reduced nitrogen species are burnt in the CO boilerwith the rest of the regenerator off gas, they can be oxidized toNO_(x), which is then emitted to the atmosphere. This NO_(x) along withany “thermal” NO_(x) formed in the CO boiler burner by oxidizingatmospheric N₂ constitute the total NO_(x) emissions of the FCCU unitoperating in a partial or incomplete combustion mode.

FCCU regenerators may also be designed and operated in a “incompleteburn” mode intermediate between full burn and partial burn modes. Anexample of such an intermediate regime occurs when enough CO isgenerated in the FCCU regenerator to require the use of a CO boiler, butbecause the amounts of air added are large enough to bring the unitclose to full burn operation mode, significant amounts of oxygen can befound in the off gas and large sections of the regenerator are actuallyoperating under overall oxidizing conditions. In such case, while gasphase reduced nitrogen species can still be found in the off gas,significant amounts of NO_(x) are also present. In most cases a majorityof this NO_(x) is not converted in the CO boiler and ends up beingemitted to the atmosphere.

Yet another combustion mode of operating an FCCU is nominally in fullburn with relatively low amounts of excess oxygen and/or inefficientmixing of air with coked catalyst. In this case, large sections of theregenerator may be under reducing conditions even if the overallregenerator is nominally oxidizing. Under these conditions reducednitrogen species may be found in the regenerator off gas along with NOX.

Various catalytic approaches have been proposed to control NO_(x)emissions in the flue gas exiting from the FCCU regenerator.

For example, recent patents, including U.S. Pat. Nos. 6,280,607,6,129,834 and 6,143,167, have proposed the use of NO_(x) removalcompositions for reducing NO_(x) emissions from an FCCU regenerator.U.S. Pat. No. 6,165,933 also discloses a NO_(x) reduction composition,which promotes CO combustion during an FCC catalyst regeneration processstep while simultaneously reducing the level of NO_(x) emitted duringthe regeneration step. NO_(x) reduction compositions disclosed by thesepatents may be used as an additive, which is circulated along with theFCC catalyst inventory or incorporated as an integral part of the FCCcatalyst.

In U.S. Pat. No. 4,290,878, NO_(x) is controlled in the presence of aplatinum-promoted CO oxidative promoter in a full burn combustionregenerator by the addition of iridium or rhodium on the combustionpromoter in lesser amounts than the amount of platinum.

U.S. Pat. No. 4,973,399, discloses copper-loaded zeolite additivesuseful for reducing emissions of NO_(x) from the regenerator of an FCCUunit operating in full CO-burning mode.

U.S. Pat. No. 4,368,057, teaches the removal of NH₃ contaminants ofgaseous fuel by reacting the NH₃ with a sufficient amount of NO.

However, aforementioned prior art has failed to appreciate an FCCprocess which minimizes the amount of NO_(x) and gas phase reducednitrogen species, e.g. NH₃, HCN, in the flue gas of an FCCU regeneratoroperating in a partial or incomplete combustion mode.

Efforts to control ammonia released in an FCC regenerator operated in apartial or an incomplete mode of combustion have been known.

For example, U.S. Pat. No. 5,021,144 discloses reducing ammonia in anFCC regenerator operating in a partial burn combustion mode by adding asignificant excess of the amount of a carbon monoxide (CO) oxidativepromoter sufficient to prevent afterburn combustion in the dilute phaseof the regenerator.

U.S. Pat. No. 4,755,282 discloses a process for reducing the content ofammonia in a regeneration zone off gas of an FCCU regenerator operatingin a partial or incomplete combustion mode. The process requires passinga fine sized, i.e. 10 to 40 microns, ammonia decomposition catalyst toeither the regeneration zone of an FCCU, or an admixture with the offgas from the regeneration zone of the FCCU, at a predetermined make-uprate such that the residence time of the decomposition catalyst relativeto the larger FCC catalyst particles will be short in the dense bed ofthe regenerator due to rapid elutriation of the fine sized ammoniadecomposition catalyst particles. The fine sized elutriateddecomposition catalyst particles are captured by a third stage cycloneseparator and recycled to the regenerator of the FCCU. The decompositioncatalyst may be a noble group metal dispersed on an inorganic support.

U.S. Pat. No. 4,744,962 is illustrative of a post-treatment process toreduce ammonia in the FCCU regenerator flue gas. The post-treatmentinvolves treating the regenerator flue gas to lessen the ammonia contentafter the gas has exited the FCCU regenerator but before passage to theCO boiler.

There remains a need in the refining industry for improved compositionsand processes which minimizes the content of gas phase reduced nitrogenspecies and NO_(x) emitted from a partial or incomplete combustion FCCUregenerator during an FCC process, which compositions are effective andsimple to use.

SUMMARY OF THE INVENTION

The essence of the present invention resides in the discovery ofparticulate compositions which are capable of being circulatedthroughout a fluid catalytic cracking unit (FCCU) along with thecracking catalyst inventory to minimize the content of gas phase reducednitrogen species, e.g. NH₃ and HCN, and NO_(x) present in the off gas ofthe FCCU regenerator when the FCCU regenerator is operated in a partialor incomplete burn mode. Advantageously, the compositions exhibit highefficiencies for the oxidation of gas phase reduced nitrogen speciespresent in the regenerator off gas to molecular nitrogen prior topassage of the off gas to the CO boiler. This reduced content of gasphase reduced nitrogen species in the off gas provides for an overallreduction of NO_(x) emitted into the atmosphere from the FCCU due to adecrease in the amount of the nitrogen species being oxidized to NO_(x)in the CO boiler as CO is oxidized to CO₂.

Despite the reducing environment in an FCCU regenerator operated in apartial burn or incomplete burn mode, some NO_(x) may form in theregenerator. In addition to reducing the content of gas phase reducednitrogen species, compositions of the invention also enhance the removalof any NO_(x) formed in the partial or incomplete burn regenerator bycatalyzing the reaction of NO_(x) with reductants typically found in theFCCU regenerator, e.g. CO, hydrocarbons, and gas phase reduced nitrogenspecies, to form molecular nitrogen. Advantageously, the compositions ofthe invention provide a reduction of NO_(x) formed in the regenerationprior to the NO_(x) exiting the regenerator and being passed unabatedthrough the CO boiler into the environment.

In accordance with the present invention, compositions of the inventionare comprised of a particulate composition which comprises (i) an acidicmetal oxide which contains substantially no zeolite; (ii) an alkalimetal, alkaline earth metal, and mixtures thereof, measured as the metaloxide, (iii) an oxygen storage component, and (iv) a noble metalcomponent, preferably platinum, rhodium, iridium or mixtures thereof. Ina preferred embodiment of the invention, compositions of the inventionare used in the FCC process as separate additives particles circulatedalong with the circulating FCC catalyst inventory.

The present invention also provides a process for reducing the contentof gas phase reduced nitrogen species released from the regenerator ofan FCCU operated in a partial or incomplete mode of combustion. Inaccordance with the present invention, the process comprises contactingunder FCC catalytic conditions the off gas of an FCCU regeneratoroperated in a partial or incomplete combustion mode with an amount ofthe compositions of the invention effective to oxidize the gas phasereduced nitrogen species to molecular nitrogen. The invention alsoprovides a process for reducing NO_(x) emissions from an FCC processoperated in a partial or incomplete combustion modes using thecompositions of the invention.

Accordingly, it is an advantage of this invention to providecompositions which are useful to reduce the content of gas phase reducednitrogen species released from an FCCU regenerator operating in partialor incomplete combustion modes during an FCC process.

It is also an advantage of this invention to provide compositions whichare useful to reduce NO_(x) emissions from an FCCU regenerator operatingin partial or incomplete combustion modes by minimizing the amount ofreduced nitrogen species emitted from the regenerator during an FCCprocess.

Another advantage of the invention is to provide compositions which areeffective to oxidize gas phase reduced nitrogen species released from anFCCU regenerator operating in partial or incomplete combustion modes tomolecular nitrogen, thereby minimizing the conversion of the reducednitrogen species to NO_(x) in the downstream CO boiler.

It is another advantage of this invention to provide compositions whichare useful to reduce NO_(x) emissions from an FCCU regenerator operatingin partial or incomplete combustion modes to molecular nitrogen bycatalyzing the reaction of NO_(x) with CO and other reductants typicallypresent in a partial or incomplete burn FCCU regenerator.

It is another advantage of this invention to provide a process for thereduction of the content of NO_(x) in the off gas of an FCCU regeneratoroperating in partial or incomplete combustion mode by reducing thecontent of gas phase reduced nitrogen species being emitted in the offgas released from the regenerator, prior to passage of the gas to a COboiler, whereby as CO is oxidized to CO₂, a lesser amount of the gasphase reduced nitrogen species is oxidized to NO_(x).

It is another advantage of this invention to provide a process for thereduction of gas phase reduced nitrogen species in an effluent gasstream passed from an FCC regenerator to a CO boiler, whereby as CO isoxidized to CO₂ a lesser amount of the reduced nitrogen species isoxidized to NO_(x).

Another advantage of this invention is to provide a process for thereduction of the content of NO_(x) in the off gas of an FCCU regeneratoroperating in a partial or incomplete combustion mode by the reduction ofNO_(x) being emitted in the off gas released from the regenerator, priorto passage of the gas to the CO boiler where the NO_(x) remainsuntreated and is eventually released into the environment.

Yet another advantage of this invention is to provide improved partialor incomplete combustion FCC processes using the compositions of theinvention.

These and other aspects of the present invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic representation of the comparison of ammoniareduction in an RTU where ammonia reacts with CO at various levels ofoxygen in a reactor feed in the presence of Additives A, B and C, thecracking catalyst alone, and a commercial combustion promoter, CP-3®.

FIG. 2 is a graphic representation of the comparison of ammoniaconversion to NO in an RTU where ammonia reacts with CO at variouslevels of oxygen in a reactor feed in the presence of the Additives A, Band C, the cracking catalyst alone, and a commercial combustionpromoter, CP-3®.

FIG. 3 is a graphic representation of the comparison of ammoniaconversion in an RTU where ammonia reacts with NO_(x) at various levelsof O₂ in a reactor feed in the presence of Additives A. B and C, thecracking catalyst alone, and a commercial combustion promoter, CP-3®.

FIG. 4 is a graphic representation of the comparison of NO_(x)conversion in an RTU where ammonia reacts with NO_(x) at various levelsof O₂ in a reactor feed in the presence of Additives A, B and C, thecracking catalyst alone, and a commercial combustion promoter, CP-3®.

FIG. 5 is a graphic representation of the comparison of NO_(x)conversion in an RTU where NO_(x) reacts with CO at various levels of O₂in a reactor feed in the presence of Additives A, B and C, the crackingcatalyst alone, and a commercial combustion promoter, CP-3®.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of this invention the term “NO_(x)” will be used herein torepresent oxides of nitrogen, e.g. nitric oxide, (NO) and nitrogendioxide (NO₂) the principal noxious oxides of nitrogen, as well as N₂O₄,N₂O₅, and mixtures thereof.

The term reduced “gas phase reduced nitrogen species” is used herein toindicate any gas phase species formed in the regenerator of a fluidcatalytic cracking unit during a fluid catalytic cracking process whichgas species contain a nitrogen having a nominal charge of less thanzero. Examples of gas phase reduced nitrogen species include, but arenot limited to, ammonia (NH₃), hydrogen cyanide (HCN), and the like.

The present invention encompasses the discovery that certain classes ofcompositions are very effective for the reduction of the overall NO_(x)emissions released from an FCCU when the FCCU regenerator is operated ina partial or incomplete burn combustion mode. The compositions of theinvention are characterized in that they comprise (i) an acidic metaloxide component which contains substantially no zeolite; (ii) an alkalimetal, alkaline earth metal and mixtures thereof; (iii) an oxygenstorage component; and (iv) a noble metal component selected from thegroup consisting of platinum, iridium, rhodium, osmium, ruthenium,rhenium and mixtures thereof.

The acidic metal oxide useful in the compositions of the invention isany metal oxide component having sufficient acidity to adsorb a base,e.g. pyridine, and the like. In accordance with the present invention,the acidic metal oxide contains no or substantially no, i.e. less than 5wt %, zeolite. Typically, the acidic metal oxide contains at least somealumina. Preferably, the acidic metal oxide contains at least 1 wt %alumina; more preferably, at least 25 wt % alumina; most preferably, atleast 50 wt % alumina. It is also within the scope of the invention thatthe acidic metal oxide may contain other stabilizing metal oxides, suchas for example, lanthana, zirconia, yttria, neodymia, samaria, europia,gadolinia and the like. In a preferred embodiment of the invention, theacidic metal oxide is selected from the group consisting of alumina,silica alumina, lanthana alumina and zirconia alumina.

The acidic metal oxide may be crystalline or amorphous. Amorphous silicaaluminas are most preferred. Where an amorphous alumina silica is used,it will have an alumina to silica molar ratio of about 1 to 50:1,preferably about 2 to 20:1.

The amount of the acidic metal oxide component present in thecomposition of the invention will typically be at least 5 wt % of thetotal composition. Preferably, the amount of the acidic metal oxidecomponent ranges from about 5 to about 98 wt %, more preferable fromabout 15 to about 95 wt % and even more preferable, from about 20 toabout 90 wt % of the total composition.

Further, the acidic metal oxide has a sufficient surface area to promotethe reduction of NO_(x) and gas phase reduced nitrogen species formed inthe flue gas of an FCCU regenerator operated in a partial or incompletecombustion mode. Typically, the acidic metal oxide has a BET surfacearea of at least 5 m²/g. Preferably, the acidic metal oxide has a BETsurface area of at 5 to 500 m²/g, more preferably about 70-250 m²/g.

Alkali metals useful to prepare the compositions of the inventioninclude, but are not limited to, sodium, potassium, cesium, lithium andthe like. Preferably, the alkali metal component is sodium. The amountof alkali metal present in the composition of the invention is typicallyat least 0.5 wt % (on a metal oxide basis). Preferably, the amount ofalkali metal in the composition ranges from about 1 to about 20 wt %,most preferably, from about 1 to about 10 wt % (on a metal oxide basis)of the total composition.

Alkaline earth metals useful to prepare compositions in accordance withthe present invention include, but are not limited to, magnesium,calcium, barium, strontium and the like. Preferably, the alkaline earthmetal is magnesium. The amount of alkaline earth metal present in thecomposition of the invention is at least 0.5 wt % (on a metal oxidebasis). Preferably, the amount of the alkaline earth metal ranges fromabout 0.5 to 60 wt %, most preferably 5 to 40 wt %, (on a metal oxidebasis) of the invention composition. It is within the scope of theinvention to use the alkali and alkaline earth metals alone or incombination.

The oxygen storage component may be any metal oxide having oxygenstorage capability. In a preferred embodiment of the invention, theoxygen storage component is a rare earth metal oxide or a transitionmetal oxide having oxygen storage capability. Suitable rare earth metaloxides include, but are not limited to, ceria, samaria, praseodymia,europia, terbia and mixtures thereof. Suitable transition metals includevanadia, manganese oxide, iron oxide, nickel oxide, copper oxide, cobaltoxide, chromia, titania, silver oxide, molybdenia, niobia, gold oxide,tungsten oxide, and mixtures thereof. In a most preferred embodiment ofthe invention at least a portion of the oxygen storage component isceria. Even more preferred is that the oxygen storage metal oxidecomponent consists essentially of ceria. It is also within the scope ofthe present invention that the oxygen storage metal oxide component maycontain other stabilizing metal oxides such as, for example, zirconiaand rare earth metal oxides typically not heretofore known in the art tohave oxygen storage capability, e.g., lanthana, neodymia, gadolinia,yttria, scandia, hafnia, and mixtures thereof.

The oxygen storage metal oxide component is preferably present as amicro dispersed phase as opposed to large bulk oxide particles or ionslocated at exchange sites in the oxide support. The amount of the oxygenstorage metal oxide present in the compositions of the invention mayvary considerably relative to the amount of acidic metal oxide.Generally, the oxygen storage component is present in the amount of atleast 0.1 wt %; preferably from about 1 to 50 wt %; most preferably fromabout 5 to about 30 wt %, of the total composition.

In general, the noble metal component is any metal of the noble groupmetals including but not limited to, platinum, palladium, iridium,rhodium, osmium, or ruthenium, rhenium, and mixtures thereof.Preferably, the noble metal component is selected from the groupconsisting of platinum, iridium, rhodium, osmium, ruthenium, rhenium andmixtures thereof. Most preferably, the noble metal component isplatinum, rhodium, iridium and mixtures thereof. Typically, the amountof the noble metal component useful in the present invention, calculatedas the metal, is at least 0.1 parts per million, preferably at least 10parts per million, most preferably at least 25 parts per million. In apreferred embodiment of the invention, the amount of the noble metalcomponent ranges from about 0.1 to 5,000 parts per million, preferablyfrom about 10 to 2500 parts per million, most preferably from about 25to about 1500 parts per million.

Additional materials optionally present in the compositions of thepresent invention include, but are not limited to, fillers, binders,etc., provided that said materials do not significantly adversely affectthe performance of the compositions to reduce the content of gas phasenitrogen species and NO_(x) under partial or incomplete combustionconditions. It is preferred, however, that the compositions of theinvention consist essentially of components (i) through (iv).

Compositions of the invention are in a particulate form and willtypically have any particle size sufficient to permit the composition tobe circulated throughout an FCCU simultaneously with the inventory ofcracking catalyst during an FCC process. Typically the composition ofthe invention will have a mean particle size of greater than 45 μm.Preferably, the mean particle size is from about 50 to about 200 μm;most preferably from about 55 to about 150 μm, even more preferred fromabout 60 to 120 μm. The compositions of the invention typically have aDavison attrition index (DI) value of about 0 to about 50, preferablyfrom 0 to about 20; more preferably 0 to 15.

While the present invention is not limited to any particular process ofpreparation, typically compositions of the invention are prepared byimpregnation of a microspheroidal particulate base material compositioncomprising components (i)-(iii) with a noble metal source. The basematerial composition may be prepared using any conventional method, seefor example, U.S. Pat. Nos. 6,280,607; 6,129,834 and 6,143,167, whichpatents teach preparing a base material composition comprisingcomponents (i)-(iii) by impregnation of a suitable acidic metal oxidesupport with precursors of components (ii)-(iii).

In one embodiment of the present invention, the base materialcomposition may be prepared by mixing, preferably with agitation, anaqueous slurry containing an amount of a peptized acidic metal oxide,e.g. a peptized alumina, sufficient to provide at least 1.0 weightpercent, preferably at least 25 wt %, most preferably at least. 50 wt %,of the peptized acidic metal oxide in the final composition, and havingfrom about 10 to about 30, preferably from about 20 to about 25, weightpercent solids, with an oxygen storage transition metal and/or rareearth metal salt, e.g. a carbonate, nitrate, sulfate, chloride salts andthe like, in an amount sufficient to provide at least 0.1 weight percentof an oxygen storage metal oxide, preferably ceria, in the final basematerial composition. Optionally, the oxygen storage transition metaland/or rare earth metal salt may also contain stabilizing amounts of astabilizing metal, e.g., zirconium and rare earth metals typically notheretofore known in the art to have oxygen storage capability, e.g.,lanthanum, neodymium, gadolinium, yttrium, scandium, hafnium, andmixtures thereof. Preferably, the peptized acidic metal oxide containingslurry also contains an amount of an alkali metal and/or an alkalineearth metal sufficient to provide at least 0.5 wt % of alkali metaland/or alkaline earth metal in the final base material composition.

An additional acidic metal oxide source, e.g. sodium silicate as asilica source, may optionally be added, with agitation, to the oxygenstorage metal containing slurry with agitation in an amount sufficientto provide at total of at least 5.0 weight percent, preferably fromabout 5 to about 98 weight percent, most preferably from about 15 toabout 95 weight percent and even more preferable, from about 20 to about90 weight percent, of acidic metal oxide in the final composition. Theoxygen storage metal oxide containing slurry is milled to reduce theparticle size of the materials contained in the slurry to 10 microns orless, preferably 5 microns or less. The milled slurry is spray dried toobtain particles having a mean particle size of greater than 45 μm,preferably from about 50 to 200 μm, most preferably from about 55 to 150μm, and calcined at a sufficient temperature and for a sufficient timeto form the corresponding metal oxides, preferably from about 400° C. toabout 800° C. for about thirty minutes to about 4 hours.

Optionally, the calcined metal oxide particles are treated with at leastone aqueous alkali metal and/or alkaline earth metal salt solution in anamount sufficient to impregnate the particles and provide at least 0.5weight percent alkali metal and/or alkaline earth metal in the finalbase material composition. Suitable salts for preparing the impregnatingsolutions include, but are not limited to, carbonates, bicarbonates,chlorides, nitrates, silicates and the like. The impregnated particlesare thereafter dried and calcined at a temperature and for a timesufficient to form the corresponding metal oxide, e.g. from about 400°C. to about 800° for about thirty minutes to about 4 hours.

The peptized acidic metal oxide containing slurry used to prepare thebase material composition may be prepared by (i) forming an aqueousslurry containing an amount of at least one acidic metal oxide,preferably alumina, sufficient to provide at least 1.0 weight percent,preferably at least 25 wt %, most preferably at least 50 wt % of thepeptized acidic metal oxide in the final composition, and having fromabout 10 to about 30, preferably, 20 to about 25, weight percent solidsand (ii) adding to the slurry an alkali base, e.g. sodium hydroxide,potassium hydroxide, sodium aluminate and the like, and/or an alkalineearth metal base, e.g. magnesium hydroxide, calcium hydroxide and thelike, in an amount sufficient to peptize the acidic metal oxide andprovide at least 0.5 weight percent alkali metal and/or alkaline earthmetal in the final base material composition. In general the amount ofalkali metal and/or alkaline earth metal base used ranges from about0.01 to 1.0 mole of alkali base per mole of acidic metal oxide,preferably 0.4 to 0.7 mole of alkali base per mole of acidic metaloxide. Thereafter the slurry is aged, preferably with continuousagitation, at a temperature and for a time sufficient to permit completepeptization of the acidic metal oxide contained in the slurry and obtaina high attrition resistant material having a Davison Index (DI) of 0 toabout 50, preferably, from 0 to about 20, most preferably, from 0 to 15.Preferably the slurry is aged from about room temperature to about 90°C. for about 30 minutes to about 4 hours. Generally, the peptizableacidic metal oxide containing slurry is prepared by contacting anaqueous solution with a peptizable acidic metal oxide. It is within thescope of the invention that the peptizable acidic metal oxide containedin the slurry will also contain stabilizing amounts of stabilizing metaloxides, such as for example, lanthana, zirconia, yttria, neodymia,samaria, europia, gadolinia and the like. Optionally, the stabilizingmetal oxides may be added in stabilizing amounts to the peptized acidicoxide containing slurry.

It is also within the scope of the invention to form the peptized acidicmetal oxide containing slurry by peptization of the acidic metal oxideusing an acid. In this case, a suitable acid, e.g. hydrochloric acid,formic acid, nitric acid, citric acid, sulfuric acid, phosphoric acid,acetic acid and the like, is added to the acidic metal oxide containingslurry in an amount sufficient to peptize the acidic metal oxide andobtain a high attrition resistant material as indicated by a DI of 0 toabout 50, preferably from 0 to about 20, most preferably from 0 to 15.In general, the amount of acid used ranges from about 0.01 to 1.0,preferably from about 0.05 to 0.6, mole of acid per mole of acidic metaloxide. Thereafter the slurry is aged as herein described above.

In a preferred embodiment of the invention, the base materialcomposition is prepared by (1) preparing an aqueous acidic metal oxideslurry having from about 10 to about 30 percent solids, (2) adding tothe slurry, preferably with agitation, a sufficient amount of an alkalibase and/or an alkaline earth metal base in an amount sufficient topeptize the acidic metal oxide and provide at least 0.5 weight percentof alkali metal and/or alkaline earth metal, measured as the metal oxidein the final base material composition, (3) aging the base peptizedacidic metal oxide containing slurry at a sufficient temperature and fora sufficient time to permit complete peptization of the acidic metaloxide in the slurry, (4) adding to the peptized slurry an oxygen storagemetal salt in an amount sufficient to provide at least 0.1 weightpercent of at least one oxygen storage metal oxide in the final basematerial composition, (5) optionally, adding to the slurry an additionalacidic metal oxide source, e.g. sodium silicate to provide silica, toprovide an additional acidic metal oxide (6) diluting the resultingslurry with water to provide a solids concentration of about 5 to 25,preferably, from about 10 to about 20, weight % of the slurry, (7)milling the slurry to reduce the particle size of the materialscontained in the slurry to 10 microns or less, preferably 5 microns orless, (8) spray-drying the milled slurry to obtain particles having amean particle size of greater than 45 μm, preferably from about 50 toabout 200 μm, more preferably from about 55 to 150 μm and mostpreferably from about 60 to 120 μm, (9) optionally drying thespray-dried particles at a sufficient temperature and for a sufficienttime to remove volatiles, e.g. at about 100° C. to about 250° C. forabout 1-4 hours, and (10) calcining the dried particles at a sufficienttemperature and for sufficient time to form the corresponding metaloxides as described hereinabove. In the most preferred embodiment of theinvention, the base material composition is prepared by sequentiallyperforming steps (1) through (10) hereinabove.

Final compositions in accordance with the invention are prepared byimpregnating the base material with an aqueous solution of at least onenoble metal salt, e.g. nitrate, chloride, carbonates and sulfates salts,amine complexes, and the like, in an amount sufficient to provide atleast 0.1 parts per million of noble metal, measured as the metal, inthe final catalyst/additive composition and thereafter drying theimpregnated particles to remove volatiles, e.g. typically at about 100°C. to 250° C. for 1 to 4 hours.

Compositions in accordance with the invention may be used as a componentof a cracking catalyst in an FCC process to reduce gas phase reducednitrogen species thereby reducing total NO_(x) emissions. In a preferredembodiment of the invention, the compositions are used in the form of aseparate particle additive which is circulated along with the maincracking catalyst throughout the FCCU. Alternatively, the compositionsof the invention are included as an additional component of the crackingcatalyst to provide an integrated cracking/NO_(x) reduction catalystsystem.

Where the invention composition is used as a separate additiveparticulate, (as opposed to being integrated into the FCC catalystparticles themselves), the composition is used in an amount of at least0.01 wt % of the FCC catalyst inventory. Preferably, the amount of theinvention composition used ranges from about 0.01 to about 50 wt %, mostpreferably from about 0.1 to about 20 wt %, of the FCC catalystinventory. As separate particle additives, compositions of the inventionmay be added to the FCCU in the conventional manner, e.g. with make-upcatalyst to the regenerator, or by any other convenient method.

Where compositions of the invention are integrated into the FCC catalystparticles themselves, any conventional FCC catalyst particle componentsmay be used in combination with the compositions of the invention. Ifintegrated into the FCC catalyst particles, the composition of theinvention, typically represents at least about 0.01 wt % of the FCCcatalyst particle. Preferably, the amount of the invention compositionsused ranges from about 0.01 to about 50 wt %, most preferably from about0.1 to about 20 wt %, of the FCC catalyst particles.

Somewhat briefly, the FCC process involves the cracking of heavyhydrocarbon feedstocks to lighter products by contact of the feedstockin a cyclic catalyst recirculation cracking process with a circulatingfluidizable catalytic cracking catalyst inventory consisting ofparticles having a size ranging from about 50 to about 150 μm,preferably from about 60 to about 120 μm. The catalytic cracking ofthese relatively high molecular weight hydrocarbon feedstocks result inthe production of a hydrocarbon product of lower molecular weight. Thesignificant steps in the cyclic FCC process are:

-   -   (i) the feed is catalytically cracked in a catalytic cracking        zone, normally a riser cracking zone, operating at catalytic        cracking conditions by contacting feed with a source of hot,        regenerated cracking catalyst to produce an effluent comprising        cracked products and spent catalyst containing coke and        strippable hydrocarbons;    -   (ii) the effluent is discharged and separated, normally in one        or more cyclones, into a vapor phase rich in cracked product and        a solids rich phase comprising the spent catalyst;    -   (iii) the vapor phase is removed as product and fractionated in        the FCC main column and its associated side columns to form gas        and liquid cracking products including gasoline;    -   (iv) the spent catalyst is stripped, usually with steam, to        remove occluded hydrocarbons from the catalyst, after which the        stripped catalyst is oxidatively regenerated in a catalyst        regeneration zone to produce hot, regenerated catalyst which is        then recycled to the cracking zone for cracking further        quantities of feed.

Conventional FCC catalysts include, for example, zeolite based catalystswith a faujasite cracking component as described in the seminal reviewby Venuto and Habib, Fluid Catalytic Cracking with Zeolite Catalysts,Marcel Dekker, New York 1979, ISBN 0-8247-6870-1 as well as in numerousother sources such as Sadeghbeigi, Fluid Catalytic Cracking Handbook,Gulf Publ. Co. Houston, 1995, ISBN 0-88415-290-1. Typically, the FCCcatalysts consist of a binder, usually silica, alumina, or silicaalumina, a Y type zeolite acid site active component, one or more matrixaluminas and/or silica aluminas, and fillers such as kaolin clay. The Yzeolite may be present in one or more forms and may have been ultrastabilized and/or treated with stabilizing cations such as any of therare earths.

Typical FCC processes are conducted at reaction temperatures of 480° C.to 600° C. with catalyst regeneration temperatures of 600° C. to 800° C.As it is well known in the art, the catalyst regeneration zone mayconsist of a single or multiple reactor vessels. The compositions of theinvention may be used in FCC processing of any typical hydrocarbonfeedstock. The amount of the composition of the invention used may varydepending on the specific FCC process. Preferably, the amount of thecompositions used is an amount sufficient to reduce the content of gasphase reduced nitrogen species in the flue gas of an FCCU regeneratoroperated in a partial or incomplete mode of combustion. Typically, theamount of the compositions used is at least 0.01 wt %, preferably fromabout 0.01 to about 50 wt %, most preferably from about 0.1 to 20 wt %of the cracking catalyst inventory.

In order to remove coke from the catalyst, oxygen or air is added to theregeneration zone. This is performed by a suitable sparging device inthe bottom of the regeneration zone, or if desired, additional oxygen isadded to the dilute phase of the regeneration zone. In the presentinvention an under-stoichiometric quantity of oxygen is provided tooperate the regeneration zone in a partial or incomplete combustionmode.

The presence of the compositions in accordance with the invention duringthe catalyst regeneration step dramatically reduces the emissions of gasphase reduced nitrogen species in the FCCU regenerator effluent. Byremoving the gas phase reduced nitrogen species from the effluent of theFCCU regenerator, significant reduction of NO_(x) emissions from the COboiler is achieved. In some cases, NO_(x) reduction up to 90% is readilyachievable using the compositions and method of the invention.

To further illustrate the present invention and the advantages thereof,the following specific examples are given. The examples are given asspecific illustrations of the claimed invention. It should beunderstood, however, that the invention is not limited to the specificdetails set forth in the examples.

All parts and percentages in the examples as well as the remainder ofthe specification which refers to solid compositions or concentrationsare by weight unless otherwise specified. However, all parts andpercentages in the examples as well as the remainder of thespecification referring to gas compositions are molar or by volumeunless otherwise specified.

Further, any range of numbers recited in the specification or claims,such as that representing a particular set of properties, units ofmeasure, conditions, physical states or percentages, is intended toliterally incorporate expressly herein by reference or otherwise, anynumber falling within such range, including any subset of numbers withinany range so recited.

EXAMPLES

The efficiency of the compositions of the invention to reduce NO_(x)and/or gas phase reduced nitrogen species from an FCCU regeneratoroperating in a partial or incomplete burn mode was evaluated in theExamples using a Regenerator Test Unit (RTU) and model reactions. TheRTU is an apparatus specifically designed to simulate the operation ofan FCCU regenerator. The RTU is described in detail in G. Yaluris and A.W. Peters “Studying the Chemistry of the FCCU Regenerator UnderRealistic Conditions,” Designing Transportation Fuels for a CleanerEnvironment, J. G. Reynolds and M. R. Khan, eds., p. 151, Taylor &Francis, 1999, ISBN: 1-56032-813-4, which description is hereinincorporated by reference.

The model reaction for determining the ability of the compositions ofthe invention to reduce gas phase reduced nitrogen species withoutconverting the species to NO_(x) in the RTU was the reaction of NH₃ overa cracking catalyst inventory containing the additive tested in thepresence of CO and various amounts of O₂. In this experiment NH₃represents the gas phase reduced nitrogen species, and CO and O₂represent the other reductants and oxidizers typically found in an FCCunit regenerator operating in partial burn. As the O₂ level in thereactor changes, the various reducing/oxidizing conditions that can beencountered from regenerator to regenerator or inside the sameregenerator can be simulated. The key measurement in this experiment inaddition to NH₃ conversion, is how much of the NH₃ is converted toNO_(x) if any. It is desirable that the latter conversion is as low aspossible for the widest range of O₂ amounts in the reactor.

The ability of compositions of the invention to convert NO_(x) in a FCCUregenerator operated in a partial or incomplete burn mode was determinedin the RTU by measuring the activity of the composition to catalyze thereaction of NO_(x) with CO. The key performance measurement in this testis the NO_(x) conversion. It is desirable to have high NO_(x) conversionto nitrogen for a wide range of O₂ amounts.

Gas phase reduced nitrogen species are reductants for reducing NO_(x)after it is formed. The ability of compositions of the invention tocatalyze this reaction while simultaneously converting the reducednitrogen species to molecular nitrogen was determined by measuring inthe RTU the activity of the compositions for converting NH₃ with NO_(x)under various O₂ levels, simulating the reducing/oxidizing conditionspossible in a regenerator operating in partial burn. Itis desirable inthis experiment to have high NO_(x) conversion to nitrogen.

Example 1

A silica-alumina slurry was prepared by adding 30 pounds of SRSIIsilica-alumina powder to 57 pounds of water that have been heated to 38IC. (SRSII sold by Grace Davison, a Business Unit of W.R. Grace &Co.-Conn., in Columbia, Md., silica-alumina powder contained 6% SiO₂,94% Al₂O₃ and had a moisture content of 33%.) The slurry was prepared ina steam-jacketed stainless steel tank fitted with an electric poweredagitator. Six pounds of an aqueous hydrochloric acid solution (35% HCl)and 6.7 pounds of an aqueous aluminum chlorohydrol solution (22% Al₂O₃)were added to the silica-alumina slurry. The mixture was heated to 55°C. and allowed to age at this temperature for 4 hours with continuousagitation. After the age period, 15.3 pounds of cerium carbonatecrystals (obtained from Rhone Poulenc, Inc., 96% CeO₂, 4% La₂O₃, 50%moisture) was added to the tank and 30 pounds of water were added to thetank to reduce the solid content of the slurry to 20 wt %.

The mixture was milled in a Draiswerke horizontal media mill of ca. 12 Lworking volume, filled to about 80% of the volume with 1.2 mm diameterglass beads. The slurry was pumped at a rate of about 2.3 liters perminute. This milling reduced the average particle size of the materialscontained in the slurry to less than 10 microns.

The milled slurry was fed to a 10 ft. diameter Bowen Engineering spraydrier fitted with a rotary atomizer. The spray drier was operated at315° C. inlet air temperature and 138° C. outlet air temperature. Theslurry feed rate was used to control the outlet air temperature. Therotational speed of the atomizer was adjusted until ˜50% of the productmicrospheres were retained on a No. 200 screen.

The spray dried product was loaded into stainless steel trays and heattreated for 2 hours at 675° C. Only enough material was loaded in eachtray so as to obtain a thin layer (˜¼ inch) of catalyst on the bottom ofeach tray.

A one-third portion of the material was then charge into a small Eirichmixer and sprayed with a aqueous solution of sodium carbonate to obtainabout 5% Na₂O in the final product. The amount of solution was adjustednot to exceed the water pore volume of the powder. The impregnatedmaterial was dried in an oven at 120° C. overnight and calcined for 2hours at 675° C. The final composition had the following analysis: 66.2%Al₂O₃, 3.9% SiO₂, 23.9% CeO₂, 1% La₂O₃, 5% Na₂O.

Example 2

An aqueous slurry of peptizable alumina was prepared by combining 27.8pounds of Versal-700 alumina powder (obtained from LaRoche Industries,Inc., 99% Al₂O₃, 30% moisture) with 52 pounds of water at roomtemperature in a well agitated tank. While mixing, 2.7 pounds of asodium hydroxide solution were slowly added to the slurry and themixture was aged for 20 minutes at room temperature. At the end of theage period, 4.5 pounds of a sodium silicate solution (27.3% SiO₂, 5.7%Na₂O) and 13.6 pounds of cerium carbonate crystals were added to theslurry. Additional water was added to the slurry to bring the solidsconcentration to 12%. The material was milled, spray dried and calcinedusing the methods described in Example 1. The final composition had thefollowing analysis: 67.4% Al₂O₃, 4.3% SiO₂, 22.9% CeO₂, 0.9% La₂O₃ and4.5% Na₂O.

Example 3

An aqueous solution was prepared consisting of 3 pounds of Lignosite-823surfactant (obtained from Georgia-Pacific West, Inc.) in 180 pounds ofwater at room temperature. Twenty six pounds of Versal-700 aluminapowder (obtained from LaRoche Industries, Inc., 99% Al₂O₃, 30% moisture)and 29.3 pounds of an aqueous formic acid solution (45% CH₂O₂) wereadded to the Lignosite solution. The slurry was allowed to age for 10minutes with continuous agitation and then 12 pounds of cerium carbonatecrystals were slowly added with continuous agitation. The slurry wasmilled, spray dried and calcined as described in Example 1 above.

The calcined product was loaded into an Eirich mixer and sprayed with aaqueous solution of sodium silicate containing 9.2% SiO₂ and 1.92% Na₂O.The impregnated material was dried in an oven at 120° C. overnight andcalcined for 2 hours at 675° C. The product was impregnated again withan aqueous solution of sodium carbonate containing 7.0% Na₂O, followedby drying and calcining as described in Example 1 above.

Example 4

A microspheriodal particulate support material was prepared as a basematerial for the preparation of a NO_(x) composition of the invention. Aslurry was prepared from an aqueous slurry having 20% solids of apeptizable alumina (Versal 700 alumina powder obtained from La RocheIndustries Inc., 99% Al₂O₃, 30% moisture). The alumina slurry wasprepared using 31.6 lbs of the alumina. To the alumina slurry 3.87 lbsof an aqueous sodium hydroxide solution (50% NaOH) was added. Next, 10.4lbs of cerium carbonate crystals (obtained from Rhone Poulenc, Inc., 96%CeO₂, 4% La2O₃, 50% moisture) was added to the slurry. The slurry wasdiluted in with a sufficient amount of water to bring the solidsconcentration of the slurry to 12%. Finally, 3.38 lbs of exchangedsilica sol of Nalco 1140 (obtained from Nalco Chemicals Co.) was addedto the slurry. The mixture was agitated to assure good mixing and thenmilled in a stirred media mill to reduce agglomerates to substantiallyless than 10 microns. The milled mixture was then spray dried asdescribed in Example 1 to form approximately 70 micron microspheres andthereafter calcined at approximately 650° C. to remove volatiles. Theresulting material had the following analysis: 2.3% total volatiles, andapproximately 4.5% SiO₂, 5% Na₂O, 16.8% CeO₂ and 73% Al₂O₃, and BETsurface area of 140 m²/g.

Example 5

A composition, Additive A, was prepared in accordance with the presentinvention using the base material prepared in Example 4. 80.0 g of thebase material was placed in an inclined beaker on a mechanical rotator.A platinum impregnation solution was prepared by weighing out 0.1715 gof an aqueous platinum tetramine dihydroxide solution (22.79% platinum)and diluting with DI water to 100 g total. The base material was thenimpregnated by gradually spraying with 50 g of the dilute Pt solutionthrough an air mist spray nozzle system. The wet impregnated basematerial was dried in an oven at 120° C. overnight. The dried cake wasin the form of large chunks and was first ground in a blender andscreened before calcining at 650° C. for two hours to decompose thenitrates and remove volatiles. The resulting material contained: 72.5%Al₂O₃, 4.4% SiO₂, 5% Na₂O, 18.8% CeO₂, 331 ppm Pt and had a BET surfacearea of 135 m²/g.

Example 6

A composition, Additive B, was prepared in accordance with the presentinvention using the base material prepared in Example 4. 80.0 g of thebase material was placed in an inclined beaker on a mechanical rotator.A master Rh solution was prepared by diluting 1.0098 g of an aqueousrhodium nitrate salt solution (10% Rh) to 77.48 g of DI water. The basematerial was then impregnated by gradually spraying with 60 g of thedilute Rh solution through an air mist spray nozzle system. The wetimpregnated material was dried in an oven at 120° C. overnight. Thedried cake was in the form of large chunks and was first ground in ablender and screened before calcining at 650° C. for two hours todecompose the nitrates and remove volatiles. The resulting materialcontained: 73.2% Al₂O₃, 4.5% SiO₂, 5.1% Na₂O, 17.5% CeO₂, 1005 ppm Rhand had a BET surface area of 127 m²/g.

Example 7

A composition, Additive C, was prepared in accordance with the presentinvention using the base material prepared in Example 4. 80.0 g of thebase material was placed in an inclined beaker on a mechanical rotator.A master Rh solution was prepared by diluting 1.0098 g of an aqueousrhodium nitrate salt solution (10% Rh) to 77.48 g of DI water. A furtherdilution was prepared by removing 5.83 g of the previously made masterdilution and adding DI water to 60 g total weight. The base material wasthen impregnated by gradually spraying with 60 g of the latter dilute Rhsolution through an air mist spray nozzle system. The wet impregnatedmaterial was dried in an oven at 120° C. over night. The dried cake wasin the form of large chunks and was first ground in a blender andscreened. The dried cake containing ˜100 ppm Rh was placed in aninclined beaker on a mechanical rotator. A platinum impregnationsolution was prepared by weighing out 0.1715 g of an aqueous platinumtetramine dihydroxide solution (22.79% Pt) and diluting with DI water to100 g total. 50 g of said solution was then impregnated onto the driedrhodium containing powder by gradually spraying through an air mistspray nozzle system. The wet impregnated material was dried in an ovenat 120° C. overnight. The dried cake was in the form of large chunks andwas first ground in a blender and screened before calcining at 650° C.for two hours to decompose the nitrates and remove volatiles. Theresulting material contained: 72.5% Al₂O₃, 4.3% SiO₂, 5.1% Na₂O, 16.9%CeO₂, 90 ppm Rh, 355 ppm Pt, and had a BET surface area or 134 m²/g.

Example 8

The activity of Additives A, B and C to reduce NH₃ in an FCC unitregenerator operating in partial burn or incomplete combustion wascompared to the activity of the cracking catalyst alone and acommercially available CO combustion promoter, CP-3® (platinum onalumina) (sold by Grace Davison, a business unit of W.R. Grace &Co.-Conn., Columbia, Md.). The experiments were conducted by reacting inthe RTU reactor NH₃ with CO at various levels of O₂, simulating partialburn. After calcination for 2 hours at 595° C., the additive was blendedat 0.5% level with FCC catalyst, which had been deactivated for 4 hoursat 816° C. in a fluidized bed reactor with 100% stream. CP-3® wasblended at 0.25% with the cracking catalyst. The cracking catalystalone, and the platinum-based CO combustion promoter Grace Davison CP-3®or the additive/cracking catalyst blend were separately fed to the RTUreactor operating at 700° C. The gas feed to the RTU was a mixture ofNH₃ and CO containing approximately 600 ppm NH₃, 5000-5500 ppm CO,various amounts of O₂ added as 4% O₂ in N₂, with the balance beingnitrogen. The total gas feed rate excluding the O₂ containing gas feedwas 1000-1100 sccm. The results are recorded in FIG. 1 and FIG. 2 below.

As shown in FIGS. 1 and 2, Additives A, B and C are very effective inminimizing NH₃ and preventing its conversion to NO_(x). No othernitrogen oxides (e.g., NO₂ or N₂O) were detected, indicating theconversion of NH₃ to molecular nitrogen. Additives B and C are the mosteffective of the three additives. The activity of additives A, B, and Cfor reducing NH₃ under partial burn conditions was far superior to thatof the conventional combustion promoter, like the commercially availableCP®-3.

Example 9

The activity of Additives A, B and C for reducing NH₃ and NO_(x) presentin an FCC unit regenerator operating in partial burn or incompletecombustion was also compared to the activity of the cracking catalystalone and a commercially available CO combustion promoter, CP-3®, usingthe reaction of NH₃ with NO_(x) under partial burn conditions. Theexperiments were conducted as in example 8 except that the gas mixturefed to the RTU reactor contained approximately 1000 ppm NH₃ and 500-550ppm NO_(x) as well as various amounts of oxygen with the balancenitrogen. The results are recorded in FIG. 3 and FIG. 4 below.

As shown in FIG. 3 and FIG. 4, compositions of the invention, i.e.Additives A, B and C, showed enhanced conversion of NH₃ and NO_(x) tomolecular nitrogen. No other nitrogen oxides, like N₂O or NO₂, weredetected during these experiments, indicating the conversion of NH₃ tomolecular nitrogen.

Example 10

The activity of Additives A, B and C to reduce NO_(x) formed in anpartial burn or incomplete burn FCCU was compared to that of thecracking catalyst alone and a commercially-available,platinum-containing combustion promoter, CP-3®, by measuring theactivity of the materials to covert NO_(x) to molecular nitrogen in thepresence of CO at various levels of oxygen. The experiments wereconducted as in Example 8 except that the gas feed to the reactor was amixture containing 5000-5500 ppm CO, 500-550 ppm NO_(x), various amountsof oxygen added as 4% O₂/N₂, and the balance nitrogen. The results arerecorded in FIG. 5 below.

FIG. 5 show that Additives A, B and C are very effective for convertingNO_(x) under partial burn conditions. They are also more effective thanthe combustion promoter at low levels of oxygen simulating partial burn.No other nitrogen oxides like N₂O or NO₂ were detected.

1-37. (Cancelled)
 38. A composition for reducing the content of NO_(x)and gas phase reduced nitrogen species during catalyst regeneration in afluid catalytic cracking (FCC) process said composition comprisingparticles having a mean particle size of about 50 to about 200 μm andcomprising (i) at least about 5.0 wt % of acidic metal oxide containingsubstantially no zeolite; (ii) a metal component selected from the groupconsisting of alkali metal, alkaline earth metal and mixtures thereof;(iii) at least 0.1 wt %, measured as metal oxide, of an oxygen storagemetal oxide; and (iv) at least 0.1 ppm of a noble metal componentcomprising palladium and at least one metal selected from the groupconsisting of platinum, iridium, rhodium, osmium, ruthenium, rhenium andmixtures thereof, said metal component (ii) being present in amount ofat least 0.5 wt %, measured as metal oxide, of the composition.
 39. Thecomposition of claim 38 wherein the acidic metal oxide is selected fromthe group consisting of alumina, silica alumina, lanthana alumina andzirconia alumina.
 40. The composition of claim 39 wherein the saidacidic metal oxide is silica alumina.
 41. The composition of claim 38wherein the acidic metal oxide further comprises at least onestabilizing metal oxide.
 42. The composition of claim 41 wherein thestabilizing metal oxide is selected from the group consisting of yttria,neodymia, samaria, europia, gadolinia and mixtures thereof.
 43. Thecomposition of claim 38 wherein the component (ii) is alkali metal. 44.The composition of claim 43 wherein said alkali metal is selected fromthe group consisting of sodium, potassium, cesium, lithium and mixturesthereof.
 45. The composition of claim 44 wherein the alkali metal issodium or potassium.
 46. The composition of claim 45 wherein the alkalimetal is sodium.
 47. The composition of claim 38 wherein component (ii)contains an alkaline earth metal.
 48. The composition of claim 47wherein the alkaline earth metal is selected from the group consistingof magnesium, calcium, barium, strontium and mixtures thereof.
 49. Thecomposition of claim 48 wherein the alkaline earth metal is magnesium.50. The composition of claim 38 wherein the oxygen storage component(iii) is a rare earth metal oxide having oxygen storage capability, atransition metal oxide having oxygen storage capability, and mixturesthereof.
 51. The composition of claim 50 wherein the oxygen storagecomponent (iii) is a rare earth metal oxide having oxygen storagecapability.
 52. The composition of claim 51 wherein the rare earth metaloxide is selected from the group of ceria, samaria, praseodymia,europia, terbia and mixtures thereof.
 53. The composition of claim 50wherein the oxygen storage component (iii) is a transition metal oxidehaving oxygen storage capability.
 54. The composition of the above claim53 wherein the transition metal oxide is selected from the groupconsisting of vanadium, manganese oxide, iron oxide, nickel oxide,copper oxide, cobalt oxide, chromia, titania, silver oxide, molybdenia,niobia, gold oxide, tungsten oxide and mixtures thereof.
 55. Thecomposition of claim 52 wherein at least a portion of the rare earthmetal oxide comprises ceria.
 56. The composition of claim 55 wherein therare earth metal oxide consists essentially of ceria.
 57. Thecomposition of claim 50 wherein the oxygen storage metal oxide component(iii) further comprises at least one stabilizing metal oxide.
 58. Thecomposition of claim 57 wherein the stabilizing metal oxide is selectedfrom the group consisting of zirconia, lanthana, neodymia, gadolinia,yttria, scandia, hafnia and mixtures thereof.
 59. The composition ofclaim 38 wherein the noble metal component is selected from the groupconsisting of platinum iridium, rhodium and mixtures thereof.
 60. Thecomposition of claim 59 wherein the noble metal component is selectedfrom the group consisting of rhodium, iridium and mixtures thereof. 61.A fluid cracking catalyst comprising (a) a cracking component suitablefor catalyzing the cracking of hydrocarbons, and (b) the composition ofclaim
 38. 62. The cracking catalyst of claim 61 wherein said crackingcatalyst comprises an admixture of components (a) and (b).
 63. Thecracking catalyst of claim 61 wherein said catalyst comprises integralparticles which contain both components (a) and (b).
 64. The crackingcatalyst of claim 61 wherein component (b) comprises at least 0.01 wt %of the cracking catalyst.